How To Use Rifle Scope

There is two main tube diameters in the marketplace plus a few other sizes:

A:The more popular 1” (25.4mm) diameter – called by many the American tube

B:The less popular 30mm (1.18”) diameter – called by many the European tube

C:A small quantity of tubes are offered in 34mm, 35mm, or larger diameters for specialized applications

What are the Differences between the 1” (25.4mm) and 30mm (1.18”) Tube Diameter?

Overall, there is not much difference:

A – Optically

There is a misconception among many in the hunting industry, including many writers, that all 30mm tubes allow more light through the riflescope, give you a larger field of view, increase light transmission in low light conditions, give you sharper images, etc. However, these comments are somewhat misleading (they do make for good marketing copy!) and in virtually all cases the image you actually see with the 30mm is no different from that with 1” tubes!

You absolutely have the same field of view, as no larger field of view is possible! The resolution of the image will remain the same in virtually all cases!

As far as getting any additional light through the system, it depends on the exact optical design of your riflescope. Let us assume for the two tube sizes that the objective size (40mm) and its design as well as the eyepiece design are identical and the variable power is 3x to 9x. The actual exit pupil is 13.33mm at 3x and 4.44mm at 9x and let us also assume the optical coatings are identical.

1.If the riflescopes both have identical erecting lens systems and do not have a field lens, then the larger 30mm tube will not gather any additional light.

2.If the 30mm tube has a larger erecting lens system than the 1” tube and neither has a field lens, then the 30mm tube may gather some additional light from the rays passing through the objective lens that were vignetted at the edge of the field of the 1” tube. Note that most 30mm tubes in the marketplace do not have larger erecting lens systems.

3.If the riflescopes both have identical erecting lens systems and do have a field lens (that refocuses the light rays from vignetting as much), then the larger 30mm tube will not gather any additional light.

For # 2 above, the additional light gain will not be noticeable at all in daylight as the exit pupil at low or high power is larger than the entrance pupil of your eye (depending on the brightness of the day it ranges from 2 to 3mm). The additional light gain in low light conditions (dusk and dawn) could benefit some younger people but I am not sure if they really can see any difference and for older people with smaller entrance pupils there probably is no benefit that can be seen.

Therefore, I am skeptical that spending additional money for a larger 30mm tube mainly for optical improvements makes any sense.

B – Mechanically

The 30mm tube diameter does add rigidity and strength (assuming the same wall thickness as the 1” tube) due to the larger cross-sectional area along with larger rings and mounts. The 30mm tube does increase the adjustment range for elevation and windage (on most riflescopes) and this is quite useful for long distance hunting.

On the negative side, the 30mm tube is heavier, larger, more prone to dents, and more expensive than 1” tubes.

Most hunters would be hard pressed to detect any performance difference between the two sizes except a little at long distances with added elevation and windage adjustments.

The growth of the 30mm tubes over the last decade has mainly been due to consumer demand associated with marketing hype from the manufacturers.

One Piece versus Two Piece Tubes

One-piece construction is the normal offering in today’s market except for some of the lower-end products. It is stronger, sturdier, and sealed better than two-piece tubes.

Two-piece tubes are generally less expensive to make as assembly time is less and machining is easier.

I would recommend only one-piece tubes due to the higher potential of leaks (gas escaping and water coming in) in two-piece tubes and because they are inferior in strength and structural design.

Tube Materials

Most riflescope tubes are made of aircraft grade aluminum, usually 6061T6. More expensive titanium tubes used mainly in military applications may be slightly lighter in weight than aluminum ones but aluminum is strong and light enough for virtually all uses. A very few tubes are made of steel. Recently, some tubes are using a magnesium alloy for added strength and a slightly lesser weight than aluminum but at an added cost.

From a structural standpoint, all of the materials are good. The wall thickness of any of the tube materials must be satisfactory to handle the rigorous functions of the riflescope.

Tube Finishes

The predominant tube finish today is a matte black. Why is this? It will come with a hard-anodized finish, which has virtually no reflections or glare. It is rugged, virtually scratchproof and immune to rust.

You will also find glossy black, silver in matte or glossy, and some other colors. In many cases, the users are trying to match the color of their rifles, handguns, etc. and this is ok for target shooting. Nevertheless, for hunting purposes, shiny finishes are not good as they are subject to glare and reflections and are likely to scare off game.

You will also find camouflage models. Camouflage was more prevalent a decade ago and is less popular now. You will find inexpensive clamshell packed models in large retailers.

A few manufacturers offer rubber covering on the tubes for a more rugged riflescope for use in extreme and unfriendly environments.

Reticles

Reticles are also called crosshairs, sighting references or graticules. Their main purpose is to allow hunters to place the aiming point within the riflescope on the animal or target. Reticle choice is very important and there are many considerations to make.

Reticles come in a multitude of configurations and can be a system of posts (thick or thin), lines, bars, circles, dots, angles, numbers, etc. in your riflescope that appear superimposed on the target. Reticles range from a simple crosshair style, to plex styles, to very complex styles (Mil Dot, etc.) to allow hunters to estimate the distance to an animal or target (if the animal or target size is known), and to compensate for bullet drop (BDC) which may be difficult to use for some hunters.

Recommending a particular reticle type is difficult to do as the hunter has to take into consideration the type of hunting he will be doing and how easy he wants it to be – in other words, it comes down to personal choice.

Basic Crosshair Reticles

Up until the 1950s, the only reticle normally used was the basic crosshair. The crosshairs were made of spider web material or metal wire and put together very meticulously. These reticles are best for many small rodents, prairie dogs and varmints since usually the hunting distance is long and they only cover up a small amount of the target, which makes the target brighter and easy to see. They are also very good for target shooting.

Plex Reticles

During the 1960s, the duplex reticle (still simple crosshairs with varying thickness of the lines and easy to use) was developed by Leupold & Stevens and became very popular. The duplex (and numerous similar or somewhat similar styles) are still very popular and are a great all-around choice for many hunters. Some manufacturers began using a photo-etching process on metal foil to make the reticles.

The plex (duplex, multiplex, and numerous other hybrids) typically have wide and thick crosshairs coming from the outer perimeter towards the center of the reticle. As the lines of the crosshairs near the center where they cross each other, the crosshairs become very narrow and fine allowing for accurate target placement. The thick crosshairs are easier to see in low light conditions or against busy backgrounds like forest or foliage. They are very good for big game hunting.

Some of the more complex designs allow for some range finding capability. Both the basic crosshair reticle and plex type reticles are now mainly manufactured using thin etched glass. The etched glass style is stronger, more reliable and has the ability to provide complex designs easily. The negative to etched glass is that some of the light passing through the glass reticle is absorbed or lost to reflection. However, multi-coatings put on the glass minimize any absorption losses.

Mil-Dot Reticles

Put simply, using a set of fixed data references within a riflescope on the reticle, a hunter can compare sizes of the target (known object height) or a part of the target to the precision dots and spaces in order to calculate the true distance. These reticles have a series of dots coming from the center of the reticle on fine crosshairs.

The “Mil” in Mil-Dot Reticle does not mean military (although the military extensively uses this type of reticle).

We use mils to find the distance to a target (where we know the height) which we need to know to aim the shot precisely. If we do not know the height of the target, then the reticle is useless.

Mil-Dot reticles calibrated at the factory are for only one magnification. In variable riflescopes, calibration is at the highest magnification.

Mil-Dot reticles are not for everyone (including me) as they take some time to understand and a lot of practice before they can be useful. Many people think they are too difficult to use, and they impair aiming due to the field of view “being cluttered” with dots, lines, circles, and numbers, etc. and this may be true. It takes time to calculate and is not the most accurate way to measure for distance. For those who do understand how to use them properly, they can be a big asset to the hunter and the military user for up to 1000 yards or meters.

The basic math may seem complex but bear with me. I have a hard time understanding and remembering this myself.

A Mil is 1/ 1000th of a radian, or milliradian.

1 mil is 36 inches @ 1000 yards or 1 meter @ 1000 meters.

There are two basic types of Mil-Dots used throughout the world. There are actually additional ones used in the former Soviet Union and in other countries but we will not discuss these here. Neither of the two basic types is better but they are just different.

The first one was (and continues to be) used by the U.S. Marine Corp where 6.2832 radians are in a circle. The math calculates out to 360/ 6.2832 = 57.3 ° per radian (6.2832 x 57.3 = 360 ° in a circle). Then, 6.2832 x 1000 = 6283.2 milliradians in a circle or 360/ 6283.2 = 0.0573 °/ milliradian (about 1/ 17th of a degree or 1/ 6283rd of a circle).

The second one is used by the U.S. Army (and most armies around the world use it), where 6400 milliradians are in a circle. The Army chose this method of radians using rounded numbers to make distance calculation easier for the users. The math calculates out to be 360/ 6.400 = 56.3 ° per radian (6.400 x 56.3 = 360 ° in a circle). Then, 6.400 x 1000 = 6400 milliradians in a circle or 360/ 6400 = 0.0563 ° milliradian (1/ 6400th of a circle).

The Marine style actually uses oblong dots rather than circular dots where the distance from the center of one dot to the center of the next dot equals 1 mil. Basic formulas, that roughly obtain the target distances (they are not exact but references), were developed by the military but the same applies to hunting:

Examples – whitetail deer height is 18 inches and is 1.25 mils on the reticle 18 x 27.78/ 1.25 = 400 yards distance Using metric conversion of 400 yards into meters = 366 meters Or the deer is 46 centimeters high and is 1.25 mils on the reticle 46×10/ 1.25 = 368 meters

Note: for animal height in the formula, use inches from the bottom of the brisket (breast or chest) to the top of the withers (ridge between the shoulder blades of a 4-legged animal). In the image here, see the circle for wither on top and brisket on bottom.

Typical height for a few animals:

Whitetail Deer 17– 19 inches (43 –48cm)

Elk – 23 to 25 inches (58 to 66cm)

Bull Elk – 32 to 34 inches (81 to 86cm)

Pronghorn Antelope 14– 16in.( 36– 41cm)

Caribou – 22 to 24 inches (56 to 61cm)

Coyote – 9 to 11 inches (23 to 28cm)

Sheep – 20 to 22 inches (51 to 56cm)

Rangefinding reticles are useful but using a laser rangefinder is much better, quicker and more accurate especially since there are so many choices now in the market. Some hunters will use Mil-Dot reticles because they want a sophisticated item and the feeling of having a military style product. At the same time, manufacturers offer these reticles because demand is high for them. To take the difficulty out of the calculations and the time it consumes, there are alternatives. One company (Mildot Enterprises at www.mildot.com in the USA) offers an analog calculator designed along the principles of a slide rule to make the calculations for you quickly. Personally, I prefer to use a laser rangefinder for distance measurements.

Mil-Dots and MOA

There is some confusion between Mils and MOA (Minutes of Angle/ Arc). Reticles are marked using Mil-Dots, while adjustment through the turrets for wind and elevation, are made in fractions of a MOA (as discussed under adjustment controls for riflescopes). The difference is 1 mil = 3.438 MOA.

Both Mil-Dots and MOA are two common ways to measure angles for units of measure of a circle. Mil dots are much more useful and precise.

The main feature of bullet drop compensation (ballistic elevation) is the compensation for gravity on a bullet’s trajectory at a given distance, which is “bullet drop”.

You need to know or estimate the distance to your target.

Bullet trajectory and how it is affected by gravity is important, as a bullet fired from a rifle on an even plane will hit the ground at the same time a baseball will hit the ground when dropped by my hand. When I throw the baseball to a person 100 yards (91.4meters) away and the aim point is his glove, I will have to aim and throw much higher to compensate for gravity’s effect or it will fall to the ground well before reaching him. How high I throw it, depends on the distance and speed I throw the ball.

Likewise, if I fire my rifle at a target 100 yards (91.4 meters) away when in a horizontal plane (with no bullet drop compensation), the bullet will land below center of the target.

BDC reticles usually have standard crosshairs or plex styles with small lines or circles on the vertical line below the center of the reticle, which is the amount of bullet drop over specific distances.

You make turret adjustments matched to your rifle, bullet caliber and weight, muzzle velocity and air density.

Note that with reticles focused on the second plane, they will work only at the magnification specified by the manufacturer whereas reticles focused on the first plane will work fine at any power.

More and more programs for BDC are available on manufacturer websites as well as smart phone apps.

In a perfect world, using BDC will allow your point of impact to be “spot on”. However, assuming you correctly made the turret adjustments required above and you have the distance to the target exactly correct, there are many variables that you are faced with – batch number of the ammunition, temperature, humidity, elevation and many other factors. Any minor change can affect the aim in a big way and the further the distance the further off you may be.

Thus, BDC reticles will help you get close to your target. You can also get closer by knowing the exact distance to the target and a laser rangefinder will help you.

Reticle Positioning – Focal Plane

Riflescopes have two focal (image) planes. The first image plane is in front of the erecting lenses, closer to the objective lens where the image plane is upside down and reversed left to right. The other image plane is behind the erecting lenses, closer to the eyepiece where the image plane is right side up and correct left to right.

If you are using a fixed power riflescope, it is irrelevant which focal plane is used.

On all variable power riflescopes, it is important which image plane the reticle is located in. The front image plane is the first focal plane (FFP) or objective image plane and the rear image plane is the second focal plane (SFP) or the eyepiece image plane. For example, the image plane shown below uses the first focal plane for the reticle location but you can see where the second focal plane is located when a riflescope uses this position for the reticle.

FFP reticle – will become larger or smaller depending on magnification changes, the same as the target. The advantage of this type of reticle placement is that when using range finding reticles (like Mil-Dots), they can be used at all magnifications with no problems. The disadvantage is that a reticle image may look great at low power but be cluttered and difficult to use at high power. Some reticles look sharp and good at high power but may be difficult to see at low power. FFP reticles are European style (mainly because they can be very useful during night hunting in many European countries) although many Americans use them.

SFP reticle – will remain the same size when magnification changes but the target will become larger or smaller. The advantage of this type of reticle placement is that the reticle always has the same look and less cluttered at high magnifications. The main disadvantage is that when using range finding reticles (like Mil-Dots), they are only precise at one particular magnification set by the manufacturer – which is usually the highest power or up to 10x. A minor disadvantage is that the point of aim shifts ever so slightly during magnification changes as the lenses move tiny amounts during this process. However, many of the manufacturers now make the erecting image/ power changing assembly more precise and sturdy, which eliminates any point of aim shifts.

SFP reticles are American style but many Europeans use this style also. The two images at the top show the difference of the enlarged reticle and object (FFP) while the two images at the bottom show the difference of the enlarged object while the reticle size stays the same (SFP).

Illuminated Reticles

Illuminated (lighted) reticles are popular with hunters (and military personnel) especially in low-light conditions as the reticles are much easier to see. They can even be helpful in full daylight for certain targets where the reticles stand out much more against thick foliage and forests.

The illuminated reticles are generally battery operated using LEDs. Red color is the most common as it least impedes the shooters night vision (for Europeans hunting in darkness) in low light conditions. Various other colors can be better under certain conditions and many are switchable between different colors.

The illuminator should be variable in brightness (most are except some very low cost units) via built-in rheostats to adjust the reticle to the appropriate light available. On some low cost units, the minimum brightness is too bright and thus not useful. These reticles add some weight and bulk to your riflescope.

The newest technology is electronically illuminated reticles. Radioactive isotopes (especially tritium elements), along with fiber optics, are seen more and more. Tritium illuminates the aiming point in low light conditions (beta rays from the tritium-hit phosphors to create the glow you see) without batteries and the fiber optics transmits the light. These new illuminating systems are more versatile than standard illumination systems.

Erector Tube Assembly

The erector tube assembly is part of a complete system that includes on most riflescopes the erector lenses, the reticle in some, springs, gimbals and many mechanical parts.

All of the parts manufactured are to very precise tolerances to ensure a movement free mechanism that will hold precisely the point of impact while changing magnification and repeatedly do this over many years even withstanding the heavy recoil of many firearms.

The slight shifting of the point of impact (causing missed shots on the target) used to be more prevalent with second focal plane reticles. However, over the last ten years or so, the erector tube assemblies have become more reliable (with better materials, better machining to tighter tolerances and are more precisely assembled and tested to ensure repeated, accurate performance).

Parallax

Parallax is a problem with riflescopes due to the fact of the long eye relief associated with them as compared to binoculars and best spotting scopes where the eye relief is relatively short and your eye( s) are up close to the eyepiece.

Parallax in optical riflescopes can be a problem. It can cause missed shots and a lot of frustration. It results from the image formed by the objective lens not being coincident with the reticle (focused exactly on the reticle plane). In other words, the target shifts as you move your head at an angle to either side (left/ right) or up and down from the center while looking through the eyepiece. To demonstrate parallax, use your thumb and any finger to make a circle (or use a toilet paper tube). Then hold your hand (or the paper tube) at arm’s length. Look through the circle at an object in a room or outside and then move your head slowly left or right and the object will move out of the circle. This is what parallax is. Most riflescopes are parallax adjusted (parallax free) by the factory at a specific distance from 50 to 150 yards (46 to 137 meters) and at longer or shorter distances some parallax appears. At whatever specific distance, the focal plane of the target and the reticle is the same even if you look through the eyepiece at an angle to the optical axis.

Parallax is not a problem at all if your eye is in the center of the riflescopes optical axis regardless of power, exit pupil size, or distance to the target. A certain amount of parallax is present in virtually all riflescopes. However, if there is noticeable movement of the target it is not ok and will cause you problems.

Parallax cannot be corrected by adding compound lenses in the optical system, as the reticle does not move along the tube axis to provide any compensation. The target images at different distances fall at various points between the objective lens and the erector lenses (this is why you have to refocus at different distances) and thus cause parallax. Usually parallax is not a problem at low powers up to 6x or 9x (depending on the particular riflescope) due to large exit pupils. Most riflescopes of 10x or larger powers have some means of quick parallax adjustments the user can make – for a description of these controls see the section on Adjustment Controls. In riflescopes of low price and/ or low quality, parallax can occur due to the reticle distance being positioned incorrectly from the objective lens, the reticle not being mounted securely, or a badly designed or manufactured objective lens.

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